1. Field of the Invention
The present invention relates to a system and method for enabling a radio node to selectably function as a router in a wireless communications network. More particularly, the present invention relates to a system and method for enabling a mobile user terminal to selectably operate as a router for other mobile user terminals in an ad-hoc packet-switched communications network based on certain criteria.
2. Description of the Related Art
In recent years, a type of mobile communications network known as an “ad-hoc” network has been developed for use by the military. In this type of network, each user terminal is capable of operating as a base station or router for the other user terminals, thus eliminating the need for a fixed infrastructure of base stations. Details of an ad-hoc network are set forth in U.S. Pat. No. 5,943,322 to Mayor, the entire content of which is incorporated herein by reference.
More sophisticated ad-hoc networks are also being developed which, in addition to enabling user terminals to communicate with each other as in a conventional ad-hoc network, further enable the user terminals to access a fixed network and thus communicate with other user terminals, such as those on the public switched telephone network (PSTN), and on other networks such as the Internet. Details of these types of ad-hoc networks are described in U.S. patent application Ser. No. 09/897,790 entitled “Ad Hoc Peer-to-Peer Mobile Radio Access System Interfaced to the PSTN and Cellular Networks”, filed on Jun. 29, 2001, and in U.S. patent application Ser. No. 09/815,157 entitled “Time Division Protocol for an Ad-Hoc, Peer-to-Peer Radio Network Having Coordinating Channel Access to Shared Parallel Data Channels with Separate Reservation Channel”, filed on Mar. 22, 2001, the entire content of both of said patent applications being incorporated herein by reference.
Although it is advantageous in an ad-hoc network for each of the user terminals to have the capability of operating as a router, it is at times desirable for a user terminal or a particular group of user terminals to refrain from performing routing operations. For example, if a user terminal's battery or power supply begins to become exhausted, the person using the user terminal may want his or her user terminal to cease operating as a router, or to only operate as a router if no other suitable router is available, to conserve battery power.
A system and method for enabling an ad-hoc network and its user terminals to perform these battery conserving operations is described in U.S. patent application Ser. No. 09/815,164 entitled “Prioritized-Routing for an Ad-Hoc, Peer-to-Peer, Mobile Radio Access System”, filed on Mar. 22, 2001, the entire content of which is incorporated herein by reference. As described in this patent application, a user terminal can broadcast to other user terminals routing table information that includes information pertaining to the condition of a battery of that user terminal. That is, the routing table information can indicate whether the battery of the user terminal has infinite life (i.e., the user terminal is connected to a constant power supply), excellent battery life (i.e., the user terminal's battery is essentially fully charged), poor battery life (i.e., the charge in the user terminal's battery is becoming low), or no battery life (i.e., the charge in the user terminal's battery is almost depleted). When a user terminal broadcasts its routing table to the other user terminals within its radio frequency (RF) range, each of those other user terminals store all or a relevant portion of this routing table information in their respective memory. Hence, the respective controllers in the user terminals can determine whether to route packetized data to a particular user terminal based on, for example, the condition of the battery of that particular user terminal, among other things.
For example, if a user terminal (source user terminal) wishes to communicate with another user terminal (destination user terminal) in the ad-hoc network, the controller of the source user terminal can determine, based on the routing table information stored in its memory, whether to send data packets to a particular neighboring user terminal for routing to the destination user terminal. If the routing table information indicates that the battery of that neighboring user terminal has an acceptable life rating (e.g., infinite or excellent life), then the controller of source user terminal can control the source user terminal's transceiver to send data packets addressed for destination user terminal to that neighboring user terminal over the appropriate data channel as can be appreciated by one skilled in the art. The transceiver of the neighboring user terminal can then operate as a router to route those data packets either directly to the destination user terminal if the destination user terminal is in the neighboring user terminals RF range, or to another neighboring user terminal in a manner similar to that described above.
However, when the controller of the source user terminal determines from the routing table information that the battery of a particular neighboring user terminal has poor life or no life, the controller of the source user terminal will control the source user terminal's transceiver to refrain from sending any such data packets to that particular neighboring user terminal. The controller will thus examine the routing table information to seek another route by which to send data packets to the destination user terminal. That is, the controller of the source user terminal can examine the routing table information stored in the source user terminal's memory which pertains to other neighboring user terminals to determine whether any of those neighboring user terminals can be used as routers to route the data packets to the destination user terminal. The controller can take into account such factors as the battery lives of the neighboring user terminals, as well as the expected quality of service (QOS) levels that can be attained, and so on. The source user terminal's controller can also determine whether a particular neighboring user terminal is incapable of acting as a router due to, for example, poor battery life, inaccessibility due to an obstacle blocking the line of sight (LOS) between the source and neighboring user terminal, or malfunction of the neighboring user terminal. As can be appreciated by one skilled in the art, this ability is referred to as the “self-healing” characteristics of an ad-hoc network as described, for example, in U.S. Pat. No. 5,943,322 to Mayor and in U.S. patent application Ser. Nos. 09/897,790, 09/815,157 and 09/815,164, referenced above.
In addition to enabling a user terminal to avoid or minimize its routing operations for battery conservation purposes, it may be desirable to disable the routing capability of individual user terminals or groups of user terminals for other reasons. Accordingly, a need exists for a more enhanced system and method for enabling user terminals to selectably operate as a router in an ad-hoc network.